The inventive subject matter relates to motor control apparatus and methods of operation thereof, more particularly, to motor starters and methods of operating the same.
Motor starters are commonly used with industrial electric motors. Typical solid-state motor starters control starting characteristics to meet application requirements, including acceleration and deceleration time, starting current and motor torque. Soft starters are commonly used to limit inrush current when the motor is first coupled to a power source. Large inrush currents may cause voltage dips that may negatively affect other loads coupled to the same source. High starting torque may also cause electromechanical shock that can damage windings and other components of the motor, as well as drive trains and other components mechanically coupled to the motor.
Soft motor starters may control voltage and/or current provided to the motor. For example, some soft starters may use silicon-controlled rectifiers (SCRs) that are connected in series between the power source and the load. During a startup process, the SCRs may be selectively gated “on” to gradually increase the speed of the motor. When the motor has reached a desired speed, a bypass contactor may be closed to bypass the SCRs and reduce losses. Operations of soft motor starters are described in “Solid-state soft start motor controller and starter,” Application Paper AP 03902001E (Eaton Corp. 2011).